The mother of castaway fisherman Jose Salvador Alvarenga has spoken of the "divine miracle" of her son's rescue and of hearing of him for the first time in 14 years.

Mr Alvarenga washed on a tiny atoll in the Marshall Islands last week after 13 months adrift in a small fishing boat.

Born in El Salvador, where his family still live, he will probably be repatriated there, said Marshall Island foreign affairs official Anjanette Kattil.

His family, including a 14-year-old daughter named Fatima who has no recollection of the father who left for Mexico before she was born, said they were looking forward to welcoming him home.

Maria Julia Alvarenga holds a picture of her son as she talks on the phone.

"It is a divine miracle, a sign that God was compassionate with our son's life," his mother Maria Julia said from her home on El Salvador's Pacific coast, tears of joy streaming down her face.

"I kept thinking that one day he would come back to us, that God wants him to return to our house."

In an interview on Tuesday, Mr Alvarenga said he had suicidal thoughts during his trip but was sustained by dreams of reuniting with his family and eating tortilla and chicken.

His mother was eager to oblige.

Jose Salvador Alvarenga as a young man

"We will make him a big meal, but we won't feed him fish because he must be bored of eating that," she said.

"We will make him a big plate of meat, beans and cheese to help him recover."

He is expected to leave the Marshall Islands on Friday for Hawaii, before travelling on to El Salvador or Mexico.

Doctors released from him hospital in the Marshalls capital, Majuro, late on Tuesday after a medical check-up found he was suffering severe dehydration and the effect of a poor diet but otherwise healthy.

The 37-year-old said he survived by eating raw fish and birds, and drinking turtle blood, urine and rainwater for 13 months, but that a teenage companion named Xiguel starved to death during the ordeal.

Mr Alvarenga says he set off on a fishing trip in late 2012 before becoming lost and drifting some 8,000-miles to the Marshalls in a small boat.

After shaving the bushy beard that grew during his months adrift, he was keeping a low profile in a local hotel on Wednesday, with two policemen guarding his room.

He is expected to hold a press conference before he leaves the Marshall Islands.

Where the fisherman was found: Ebon Atoll in the Pacific Ocean. Pic: Nasa

The stockily-built fisherman appeared remarkably healthy just days after being found wandering disorientated and clad only in ragged underpants on the coral atoll where his boat washed up.

There were some contradictions regarding dates in various media interviews he has given since being rescued, but authorities in Mexico confirmed they launched an air and sea search for him and a missing boy in November 2012.

Fishermen in Mexico's southern Chiapas state also said they remembered Mr Alvarenga, who was known by the nickname "La Chanca" or "fatty".

"We are surprised, but there is no doubt it's him," said fisherman William Uscanga after seeing a picture of the castaway.